In the aftermath of the Assad regime's barbaric gassing of men, women and children, President Trump declared from the Rose Garden, "When you kill innocent children, innocent babies -- babies, little babies -- with a chemical gas that is so lethal ... that crosses many, many lines, beyond a red line."

This was a reference to Barack Obama's infamous -- and infamously unenforced -- "red line" statement from 2012, in which he strongly suggested that if Syrian President Bashar Assad used chemical weapons in his effort to destroy rebel forces, America would intervene. Then Assad used chemical weapons, and Obama dithered. Syria has since become an abattoir, and Assad has slowly gained the upper hand, thanks largely to assistance from the Russians and Iranians.

During his campaign, Trump rightly excoriated Obama for squandering American credibility. But Trump also repeatedly insisted that America would not get involved in conflicts that weren't any of our business.

It remains to be seen what Trump will actually do as a consequence of these multiple line drawings, but it seems clear that he intends to do something, or at least he wants to leave that impression.

That seemed to be the point of Ambassador to the United Nations Nikki Haley's powerful presentation at the U.N. this week, in which she suggested that it may be necessary for the U.S. to act unilaterally in Syria. (Full disclosure: My wife works for Haley.)

I am sympathetic to the Trump administration's disgust with the Assad regime. And I am open to, if skeptical of, any measures that could improve the situation on the ground. If we could dispatch a drone that rendered Assad a fine pink mist without starting a war with Russia or handing Syria over to al-Qaida, I'd be all for it. Some people just need killing.

But if we've learned anything from the last few decades in the Middle East, it's that nothing there is easy and good motives don't necessarily yield good results. The Iraq War, which I supported, is hardly an experience anyone would like to repeat.

Likewise, the Obama administration's intervention in Libya hasn't exactly yielded a better, safer world or region. Libya today is a failed state and a safe haven for ISIS. Moreover, by toppling Muammar Gadhafi after he had complied with our demands to hand over his weapons of mass destruction, the Obama administration sent the message that it doesn't pay to play ball with the West. Despots are better off having WMDs they can threaten us with, as the North Koreans and Iranians firmly believe.

But what is true of interventions can also be true of non-interventions. However much of a mistake the Iraq War was, Obama's decision to turn his back on Iraq made things worse, not least by making it easier for ISIS to metastasize. The debacle of the Libyan intervention was a major reason for the Obama administration's hands-off approach toward Syria.

It's unknowable whether intervention of some kind in 2013 would have yielded a better result in Syria than what we have today. But if intervention is in the cards, as it seems to be, it probably would have been better to do it then than now. The "good" rebels were stronger and more plentiful then than they are today. Assad was weaker. Russia and Iran were less dug in. And, not least important, hundreds of thousands of Syrians were still alive, and millions more were not living in ideologically fetid refugee camps, or trying to flee into Europe.

Ultimately, the crisis facing the Trump administration exposes the impotency of so-called "realism" in the real world. Realists tend to claim that they are uniquely concerned with pursuing rational policies solely in our national interest. This is nonsense, given that all foreign policy schools claim the national interest as their lodestar, and determining the national interest is an inherently ideological enterprise. More to the point, so-called realism tends to be defenseless against the shock of events.

Obama came into office promising to be a realist, albeit of a liberal sort. In 2007, he said that preventing a potential genocide wasn't a good enough reason to stay in Iraq. But in 2011, he said intervening in Libya was justified because Gadhafi was killing thousands. Why the change? It's hard to be president when the horrible images and the shouts of "Do something!" start rolling in.

That's a lesson Trump, who also campaigned as a realist and non-interventionist, is learning. I hope he chooses wisely.